Why do the Earth and Moon turn counter-clockwise and our clocks turn clockwise?

First of all, the Earth and Moon only turn counter-clockwise when viewed from a certain perspective: above the North Pole. If you looked at them from the South Pole, they would appear to turn clockwise.

The reason that clocks turn clockwise has to do with sundials, which were the first clocks. In the northern hemisphere, the earth rotates counter-clockwise, which means that from our point of view the sun appears to move across the sky in a clockwise directon. Therefore, if you build a sundial to tell time, the shadows will move across it in a clockwise direction.

With mechanical clocks, you could of course make them go around either way, but the earliest ones were presumably designed to turn the same way the shadows on a sundial do, simply because that's what people were used to.

What this means, by the way, is that if mechanical clocks had originated in the southern hemisphere, the ones we use today would probably go around in the other direction!

About the Author

Dave is a former graduate student and postdoctoral researcher at Cornell who used infrared and X-ray observations and theoretical computer models to study accreting black holes in our Galaxy. He also did most of the development for the former version of the site.

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